The present invention relates to a substrate polishing apparatus for polishing a substrate to be polished, including a semiconductor wafer and so on. More particularly, the present invention relates to a substrate polishing apparatus having a film thickness monitor device for continuously monitoring a state of a film thickness of a thin film on a surface to be polished of the substrate (including but not being limited to the state of the film thickness and a state of the film thickness remaining on the surface) in real time during polishing with the substrate polishing apparatus.
Conventional techniques for monitoring a film thickness of a thin film on a substrate for use with a substrate polishing apparatus of the type polishing a substrate include, for example, a film thickness monitor device for monitoring a film thickness of the thin film on a substrate, as disclosed in JP-A-2001-235311 (Japanese Patent Public Disclosure). This apparatus is configured to monitor a film thickness of a thin film on the surface of a substrate on the basis of an intensity of reflected light. Water flows in a columnar form along the surface of the substrate to be polished, and the surface thereof is irradiated with an irradiation light, and the irradiated light is reflected from the surface through the flow of water to be received by an optical fiber.
One aspect of a conventional substrate polishing apparatus is constructed as decribed above. However, a problem exists with such an art in that water flowing in columnar form over a surface to be polished is not stable at a contact point with the surface and tends to vary, thus making it difficult to reliably and accurately monitor a film thickness of a thin film on the surface of the substrate film using reflected irradiated light.
As a similar technique, there is proposed a polishing-end-point detection mechanism as disclosed in JP-A-2001-88021. This mechanism is composed of an optical fiber mounted in a depression in the surface of the table so as to face a light-irradiating and light-receiving surface at one end thereof, and a flow path for feeding a washing liquid, the path having one end opening in the depression. By this configuration, while the washing liquid is being fed into the depression through the flow path, the surface to be polished of a wafer is irradiated with light through the washing liquid in the depression from the optical fiber, and the light reflected on the surface is received through the washing liquid and the optical fiber in the depression. The polishing-end-point is then detected on the basis of surface information about the surface of the substrate obtained from the reflected light.
However, a problem also exists in this art in that a washing liquid may flow in the depression in an irregular way when fed through the flow path. This is particular problem when the washing liquid is fed through a porous member. In such a case, polishing grains contained in a polishing liquid, polished chips of the wafer, polished chips of a polishing pad, and so on enter the depression, and obstruct transmission and reception of irradiated light. Thus, information about the surface of the substrate cannot be obtained with high accuracy.
It is an object of the present invention to overcome the stated problems of the conventional arts, and to provide a substrate polishing apparatus with a film-thickness monitoring device capable of monitoring a state of a film thickness of a thin film on a surface of a substrate to be polished with high accuracy and relaiability during a polishing operation.
To achieve the stated object, the present invention in a first aspect provides a substrate polishing apparatus for polishing a substrate to be polished by means of a relative movement between the substrate and a polishing member, which comprises a table, the polishing member fixed on top of the table, a substrate support member for pressing the substrate to be polished onto the polishing member; an optical system composed of an optical fiber for irradiating the surface of the substrate with a light through a through-hole disposed in the polishing member, and an optical fiber for receiving the reflected light reflected from the irradiated light on the surface through the through-hole.
The substrate polishing apparatus further comprises: an analysis system for analyzing the reflected light received by the optical system; and a film-thickness monitoring device for monitoring a film thickness of a thin film formed on the surface of the substrate, and a state of progress of polishing the thin film on the surface thereof on the basis of an analysis of the reflected light by means of the analysis system, wherein the table is provided with a liquid-feeding opening for feeding a translucent liquid to the through-hole disposed in the polishing member, the liquid-feeding opening being disposed so that the translucent liquid fed to the through-hole through the liquid-feeding opening flows in a direction roughly perpendicular to the surface of the substrate, i.e., to form a perpendicular flow which fills the through-hole, with the optical fiber being disposed such that the irradiated light and the reflected light pass through a flow portion of the translucent liquid flowing in the direction generally perpendicular to the surface.
Thus, in the configuration of the substrate polishing apparatus in the first aspect of the invention, through-holethrough-hole the surface of the substrate is irradiated with light through a flow portion of the translucent liquid flowing in the direction generally perpendicular to the surface, and the irradiated light reflected from the surface is received through the perpendicular flow of the translucent liquid. Accordingly, particles of foreign materials, including polishing grains contained in the polishing liquid, polished chips of the polishing member or the substrate, etc., cannot enter the perpendicular flow portion of the translucent liquid from a gap between the polishing member and the surface so that the film thickness of the thin film on the substrate can be observed with high accuracy and stability without intervention from those particles.
It is to be noted herein that the translucent liquid to be fed through the liquid-feeding opening may include, but is not limited to, a transparent liquid having a high transparency which is highly transparent immediately after the supply into the through-hole but may become turbid while flowing due to contamination with a polishing liquid. Therefore, the translucent liquid as referred to herein may include, but is not limited to, any transparent or translucent liquid ranging from a transparent liquid having a high degree of transparency to a translucent liquid having a low degree of transparency.
In a second aspect of the invention, the substrate polishing apparatus in the first aspect of the invention is further constructed such that the through-hole has a section extending in a direction perpendicular to a flow of the translucent liquid that is equal in size to the liquid-feeding opening and in fluid communication therewith.
As the through-hole and the liquid-feeding opening have equal sections extending in the direction perpendicular to the liquid flow and are communicated with each other, the translucent liquid fed from the liquid-feeding opening into the through-hole flows in the direction perpendicular to the surface of the substrate to be polished up to the surface. Therefore, even in a small amount, the flow of the translucent liquid is able to serve as a suitable optical path for passage of the irradiated light and the reflected light.
The substrate polishing apparatus in a third aspect of the invention is characterized in that the substrate polishing apparatus in the first or second aspect of the invention is further provided with a liquid-discharging groove on the surface of the polishing member, the liquid-discharging groove being for discharging the translucent liquid rearward from the inner side face of the through-hole in the direction of movement of the table.
As the liquid-discharging groove is provided on the upper surface of the polishing member for discharge of the translucent liquid from the inner side faces of the through-hole rearward, and in the direction of movement of the table, the translucent liquid filled in the closed space of the through-hole can be withdrawn readily from the inner side face of the through-hole without the need for any special system.
The substrate polishing apparatus in a fourth aspect of the invention is constructed such that the substrate polishing apparatus in the first aspect of the invention is further provided with a liquid-discharging opening for discharging the translucent liquid in the through-hole, which is located behind the liquid-feeding opening in the direction of movement of the table and has an opening at the side face of the through-hole opposite to the substrate to be polished.
As the substrate polishing apparatus in the fourth aspect of the invention has the liquid-discharging opening behind the liquid-feeding opening in the direction of movement of the table and has an opening at the side of the through-hole opposite the substrate, in the manner as described above, the translucent liquid within the through-hole can be withdrawn into a gap between the substrate and the polishing member without diluting the polishing liquid present therein. Further, the provision of the liquid-discharging opening behind the liquid-feeding opening in the direction of movement of the table enables a a flow to form of the translucent liquid fed from the liquid-feeding opening into the through-hole, that is, it allows the translucent liquid to flow in the direction perpendicular to the surface of the substrate, in a manner as will be described hereinafter in more detail.
In a fifth aspect of the invention, the substrate polishing apparatus is characterized in that the substrate polishing apparatus in the fourth aspect of the invention is further arranged such that the middle point of a line segment connecting the center of the liquid-feeding opening and the center of the liquid-discharging opening is located before the central point of the through-hole in the direction of movement of the table.
As a result, the translucent liquid fed from the liquid-feeding opening into the through-hole is able to form a flow perpendicular to the surface of the substrate in a manner as will be described hereinafter in more detail.
The substrate polishing apparatus in a sixth aspect of the invention is constructed such that the substrate polishing apparatus in the fourth or fifth aspect of the invention is further provided with the through-hole in a generally elliptic section in such a manner that a circumference of the external end thereof is disposed so as to enclose the end faces of the liquid-feeding opening and the liquid-discharging opening.
As the generally elliptic section of the through-hole for the substrate polishing apparatus in the sixth aspect of the invention is disposed to enclose the end faces of the liquid-feeding opening and the liquid-discharging opening in the manner as described above, the area of the through-hole can be minimized to thereby reduce its influence upon polishing characteristics.
In a seventh aspect of the invention, the substrate polishing apparatus is characterized in that the substrate polishing apparatus in any one aspect of the fourth to sixth aspects of the invention is further provided with a forced liquid discharge mechanism to thereby enable forced discharge of liquid from the liquid-discharging opening.
Accordingly, the translucent liquid can be withdrawn reliably from the liquid-discharging opening without using a liquid-feeding tube or a liquid-discharging tube or without an application of a resistance between the polishing member and the surface of the substrate to be polished.
Further, the substrate polishing apparatus in this aspect is able to form an optical path through which the irradiated light and the reflected light can pass, as well as reduce any influence on polishing characteristics, and further avoids the need for a complicated control mechanism, because an amount of the translucent liquid to be fed can be increased by providing an appropriate valve mechanism in combination with the liquid supply system. Thus, in a case where the through-hole is covered by a substrate thereby decreasing an amount of transluscent liquid supplied, or in a case that the amount of the liquid is otherwise reduced, a force for generating a negative pressure in the through-hole can be generated through the through-hole. Moreover, a constant liquid discharge effect can be exerted on the translucent liquid fed to the through-hole, and an influence upon polishing characteristics can be reduced, even in a state where the through-hole is not closed with the substrate to be polished.